Such articulated robotic arms are used particularly in situations wherein the arm is required to follow a path to a worksite with the body of the arm remaining on the path. This is known as “tip following”, with the arm advancing along the path taken by the tip, in a snake-like manner. The tip may for example carry a work tool for carrying out a task.
A known type of device is described in our co-pending application WO 0216995. In such an arm, the links are grouped into segments each comprising a plurality of links, and the shape of the arm is controlled by control cables passing through the peripheries of the links. A set of cables evenly spaced around the links, for example 3, terminates at the most distal link of each segment, such that each set of cables may be used to control the orientation of that link, and thus the shape of the segment. The links each have a central aperture, which apertures together form a channel or lumen for carrying services usually associated with the work tool, for example cables controlling the tool or for communicating with the tool.
As the cables are located at the periphery of each link, the central channel or lumen may be relatively large. Since it is coaxial with the arm, the service cables will have a minimum effect on the bending and torsional stiffness of the arm.
In some types of arm, such as that described in our co-pending application WO 070774, a helical spring is provided around the central lumen, which provides stiffness to the arm so that it tends towards a straight configuration. The arm may be constructed by engaging the links one-by-one with the helical spring and screwing them down onto the adjacent link. The control and service cables may then be threaded through the apertures in the links.
With such arms, the shape of the arm can be detected or measured in various ways, as described in our copending application no WO 0613682. This usually involves mounting measuring devices around the periphery of the links to measure the space between adjacent links.